Quantitative proteomics reveals reduction of endocytic machinery components in gliomas

Abstract

Background Gliomas are the most frequent and aggressive malignancies of the central nervous system. Decades of molecular analyses have demonstrated that gliomas accumulate genetic alterations that culminate in enhanced activity of receptor tyrosine kinases and downstream mediators. While the genetic alterations, like gene amplification or loss, have been well characterized, little information exists about changes in the proteome of gliomas of different grades. Methods We performed unbiased quantitative proteomics of human glioma biopsies by mass spectrometry followed by bioinformatic analysis. Findings Various pathways were found to be up- or downregulated. In particular, endocytosis as pathway was affected by a vast and concomitant reduction of multiple machinery components involved in initiation, formation, and scission of endocytic carriers. Both clathrin-dependent and -independent endocytosis were changed, since not only clathrin, AP-2 adaptins, and endophilins were downregulated, but also dynamin that is shared by both pathways. The reduction of endocytic machinery components caused increased receptor cell surface levels, a prominent phenotype of defective endocytosis. Analysis of additional biopsies revealed that depletion of endocytic machinery components was a common trait of various glioma grades and subclasses. Interpretation We propose that impaired endocytosis creates a selective advantage in glioma tumor progression due to prolonged receptor tyrosine kinase signaling from the cell surface. Fund This work was supported by Grants 316030-164105 (to P. Jenö), 31003A-162643 (to M. Spiess) and PP00P3-176974 (to G. Hutter) from the Swiss National Science Foundation. Further funding was received by the Department of Surgery from the University Hospital Basel.

Endocytic Adaptor Proteins in Health and Disease: Lessons from Model Organisms and Human Mutations

“…As discussed also in later sections, many endocytic adaptors have links to cancer due to the aberrant signaling that is caused by their misregulation. In line with this, a recent study using quantitative proteomics revealed that AP-2α, AP-2β and AP-2σ and also other endocytic factors exhibit decreased expression levels in gliomas [48]. In addition to effects via its endocytic function, AP-2 could also modulate tumor cell migration and invasion by its non-canonical role in microtubule acetylation as recruiter of α-Tubulin Acetyltransferase (αTAT1) which affects directional cell locomotion and chemotaxis [49].…”

“…Increasing the surface level of the respective tumor marker would improve the efficiency of the therapeutic approach. [40]; AP2S1 del17 mouse: embryonic lethality; neuron-specific AP2M1 KO: neurodegeneration and premature death [38]; IHC-specific AP2M1 KO: hearing deficit [12] AP2M1 mutation: epileptic encephalopathy [3]; AP2S1 mutation: familial hypocalciuric hypercalcemia type 3 [43]; AP-2α, AP-2β, AP-2σ downregulated in gliomas [48]; AP2A1, AP2A2 association with AD [47] Constitutive KO: behavioral alterations, epileptic seizures, premature death [105] Link to psychotic bipolar disorder [125] and to ASDs [126]; downregulated in gliomas [ Constitutive KO: increased cholesterol levels [230,231], altered ROMK response [235]; ARH/Dab2 DKO: pronounced hypercholesterolemia [256] Mutated in Autosomal recessive hypercholestero-lemia (ARH) [1] Arrestin1 (SAG) pSer/pThr in GPCR-NT Rhodopsin [295] Constitutive KO: extended response to light [295] Mutated in Oguchi syndrome: night blindness and sometimes retinal degeneration [300] Arrestin4 (ARR3)…”

“…There are no known disease mutations in Stonin genes to date, however the Stonin2 gene STON2 lies within a chromosomal region that has been associated with Tourette syndrom [78] and has also been linked to schizophrenia in one study [79] underlining the potential importance of Stonins for brain physiology in humans. Furthermore, the expression level of Stonin1 was found altered in glioma biopsies [48].…”

Clathrin- and dynamin-dependent endocytosis limits canonical NF-κB signaling triggered by lymphotoxin β receptor

“…It is likely that keeping the receptor amounts at the PM at relatively low levels minimizes unnecessary stimulation of the receptor at the cell surface by subthreshold stimuli. It was proposed that the impairment of endocytic machinery found in glioma cells might lead to prolonged RTK-dependent signaling [ 82 ]. In case of LTβR, endocytosis via multiple routes could constitute a mechanism of protection against over-activation of LTβR-evoked pro-inflammatory responses, that can be detrimental if not controlled [ 83 ].…”

Putting Proteomics Into Immunotherapy for Glioblastoma

“…An unbiased quantitative proteomics analysis of human glioma biopsies revealed that up- or downregulation could be observed in multiple pathways. For instance, both clathrin-dependent and -independent endocytosis would be affected by a large reduction in various mechanical components related to the initiation, formation, and rupture of endocytic vectors, such as clathrin, AP-2 adaptins, and endophilins ( 105 ).…”